Abstract: The rainfall loss characteristics of urban underlying surface is the most basic and most important content of urban hydrology research. With a university in Xiqing District, Tianjin as the study area, and on the basis of measured infiltration loss and evaporation loss, which are two components of rainfall losses, of five typical underlying surfaces, we investigated the rainfall loss characteristics of urban underlying surface using the scenario analysis on five representative rainfall events. Results manifested that: 1) the initial infiltration rates of green land, asphalt concrete pavement, and brick pavement were 5.28 mm/min, 1.03 mm/min and 0.61 mm/min, respectively, while asphalt concrete pavement and SBS roofing were impermeable to water. 2) The rainfall losses on green land, asphalt concrete pavement, and brick pavement were infiltration losses, whereas evaporation and other losses were negligible; for the other two impervious underlying surfaces, infiltration loss was not observed, while evaporation and other losses could not be ignored. 3) On green land, runoff yield by excessive infiltration was only formed after about 50 min of heavy rainstorm events, 40 min and 10 min after heavy rainstorm and very heavy rainstorm respectively on asphalt concrete pavement, and 15 min, 20 min, and 5 min in rainstorm, heavy rainstorm and very heavy rainstorm events respectively on brick pavement. 4) Rainfall yielded rapidly on Terrazzo pavement and SBS roofing regardless of the rainfall type due to small losses.

Key words: urban underlying surface, runoff yield and concentration, infiltration loss, evaporation loss, Tianjin